Incomplete Dominance vs.Codominance

There are two special types of inheritance: Incomplete Dominance and Codominance

Incomplete Dominance – A heterozygous situation where the two different alleles blend together.

One parent flower is red (CR CR). The other parent is white (Cw Cw).

CR CR

CW

CW

CRCW CRCW

CRCW CRCW

CRCR = 0/4 =

0% = CRCW = 4/4

= 100% = CWCW= 0/4

= 0% =

PinkRed

White

One parent flower is Pink (CR CW). The other parent is Pink (CR CW).

CR CW CR

CW

CRCR CRCW

CRCW CWCW

CRCR = 1/4 =

25% =CRCW = 2/4

= 50% = CWCW= 1/4

= 25% =

PinkRed

White

The second type of special inheritance is called codominance.

Codominance – A heterozygous situation where the two different alleles are equally dominant and they both get expressed.

One parent horse is black (FB FB). The other parent is white (FW FW).

FB FB

FW

FW

FB FW FB FW

FB FW FB FW

FB FB = 0/4 =

0% = FB FW = 4/4

= 100% = FW FW= 0/4

= 0% =

SpottedBlack

White

One parent horse is black (CB CB). The other parent is spotted (CB Cw).

CB CB

CB

CW

CBCB CBCB

CBCW CBCW

CBCB = 2/4 =

50% = CBCW = 2/4

= 50% = CWCW= 0/4

= 0% =

SpottedBlack

White

To review: Codominance happens when both alleles are

equally dominant and both alleles get expressed.

Incomplete dominance happens when the heterozygous alleles get blended.